1. Field Of The Invention
This invention relates to check valves and to magnetically operated check valves and, in one aspect, to such a valve which is stable and durable in severe and extreme environments.
2. Description of Related Art
Check valves can be found in numerous industrial, aerospace and military applications where dependable operation, under demanding conditions, is critical. Such valves have an internal port or seat through which the fluid flows and a poppet, ball, reed, or gate that covers the seat to block flow in the reverse direction (see, e. g. the valve shown in FIG. 1). Fluid flow in the desired (forward) direction pushes the poppet open when the pressure differential across the valve is sufficient to overcome the force(s) restraining the poppet. Check valves utilize a spring, gravity, or magnetic force to return the poppet to the seated (blocking) position when there is no differential pressure. If the fluid flow attempts to reverse direction, the poppet is returned to the closed position, thus checking flow. All valves require a certain amount of seating stress to effect a seal when differential pressure in the reverse direction is low. The harder (more firm) that the seal material is the greater the load has to be to provide this stress. Reed poppets do not require a separate spring as the reed itself is a spring, and returns to the seated position when forward flow forces are no longer present. However, reed poppets are not found in fluid system check valve applications due to other performance limitations.
In a spring operated check valve, the valve's poppet and spring (see FIG. 1) form a classic spring-mass system that is subject to harmonic oscillation caused by flowing fluid. Harmonic motion (oscillations of the poppet) sustained for long periods of time can result in accelerated wear. Oscillations at frequencies even higher than the natural frequency are common in gaseous fluid service. A valve that ordinarily would be expected to operate for years can be ruined in a matter of hours when operating at conditions supporting this motion. Accelerated wear of the poppet and guide results in accelerated particulate generation. Companion components in the fluid system may be rendered inoperative by the abnormally high level of particulates generated by the check valve. Excessive particulates will contaminate fluids and increase the risk of decomposition or other adverse chemical reaction.
In certain prior art valves, self sustaining motion disturbs the fluid media flowing through the valve, setting the stage for undesirable secondary effects on other components or processes in the fluid system. In other prior art, gravity operated check valves must be positioned in a manner that permits gravitational forces to return the poppet to the seated position. This limitation eliminates many applications, especially aircraft and space flight. In certain spring-operated prior those in art valves, the load that provides the necessary seating stress with the valve seated/closed is imparted with the spring in the most extended position. Thus, as the valve strokes, this bias load is additive to the normal increase in spring load that occurs as the spring is compressed to provide a flow path and increases the differential pressure across the valve.
U.S. Pat. No. 3,026,903 to Roach discloses a magnetic check valve which includes a magnetically actuated return means for the valve element, a valve cage, a permanent magnet and a magnetically permeable closure member. The check valve incorporates a ball-type closure or poppet riding in a cage lined with longitudinal magnetic rods which urge the ball toward (in the same direction as reverse flow would occur) a valve seat to prevent reverse flow. The valve has a hard metal seat and a hard ball-type poppet that seal by direct contact with one another.
U.S. Pat. No. 3,495,620 to Raimondi et al. shows a magnetic valve which includes a movable valve member of magnetic material positioned between two magnetic inlet/outlet orifices. The valve incorporates dual magnets, one movable element and two fixed, one on either side of the movable element or poppet. Once a predetermined pressure has been established, the poppet is dislodged from the seated position and normal flow entering the valve passes through a port (that comprises the valve seat) in the first magnet and through matching holes in the poppet and final fixed magnet to the valve outlet. The magnet seats and the poppet seal by directly contacting one another. The magnet that comprises the seat is subject to deposition of magnetically attracted particles carried in the flow stream. The particles can lodge between the magnetic seat element and the magnetic movable element thus preventing closure of the valve.
U.S. Pat. No. 4,874,012 to Velie teaches a magnetically operated flow device which includes a movable member between magnets that define the flow passage. The valve has a magnet upstream of the seat area which may attract some but not all magnetic particles to itself before they reach the critical area of the seat/poppet interface where sealing takes place.
U.S. Pat. No. 2,539,316 to Jerman discloses a safety valve which includes a steel ball check valve positioned adjacent a magnet. The valve acts to close in case of excess flow in a line in which the valve is installed. A magnet holds a ball away from a seat through which flow must pass. Flow in excess of the normal range of flow dislodges the ball and carries it to the seat where it blocks flow. Thus it acts like a flow fuse rather than a check valve.
U.S. Pat. No. 2,646,071 to Wagner shows a magnetic check valve which includes a movable member having a magnet therein adjacent another magnet. The valve has a plastic seat and disc (poppet) sealing by direct contact with one another. The valve is configured to catch all particles as they enter the valve.
U.S. Pat. No. 2,667,895 to Pool et al. discloses a magnetically biased check valve which includes movable and stationary magnets. The magnetically actuated check valve incorporates dual magnets working in opposition to provide a separating force that moves one of the magnets toward the seat and sealing ring; the other magnet is anchored in the valve body. Flow in the direction that assists in separating the magnets (reverse to normal flow) also assists in placing the magnet against the seat and seal, thus checking flow. The seat o-ring is embedded in the valve body. The conventional way to embed or attach an o-ring to a surface is to use a dovetail groove into which an o-ring is forced. With this type of installation there is no room for the o-ring to grow in case of thermal expansion or in case of o-ring swell (due to exposure to certain fluids). When the o-ring is not allowed to grow uniformly, it will be distorted or damaged and will no longer be effective. The seating magnet is subject to deposition of magnetically attracted particles carried in the flow stream. The particles can lodge between the magnet and valve seat thus preventing closure of the valve. The seating forces in the valve are low, and therefore sealing forces are also low at low reverse differential pressures. The valve is not configured to provide maximum magnet seating forces at the seated position to reduce leakage at low reverse differential pressures. Since the seating forces in the valve increase with displacement of the magnet (poppet) from the seat, the valve can chatter as does a spring actuated valve. The valve will augment flow-induced harmonic motion since it stores and returns energy to the moving mass of the poppet as does the spring-mass system of the conventional spring loaded poppet.
U.S. Pat. No. 2,949,931 to Ruppright shows a magnetic check valve having a magnetic cage with the moving valve member contained therein. The valve has a magnet comprising the inlet flow path and seat of the valve, and a loosely guided disc that acts as the poppet to preclude reverse flow. The magnet that comprises the seat in this configuration is subject to deposition of magnetically attracted particles carried in the flow stream. The particles can lodge between the magnet and the valve disc (poppet) thus preventing closure of the valve. A magnetic seat and the disc seal by directly contacting each other.
There has long been a need for a magnetically operated check valve which does not augment flow-induced harmonic oscillation and in which poppet wear is reduced. There has long been a need for such a valve in which energy consumption is reduced and particulate generation is minimized. There has long been a need for such a valve in which required seating stresses are effectively achieved without adding to the differential pressure of the valve at full flow conditions.